The navigation of vehicles in low-visibility conditions such as darkness, fog, low-hanging clouds, rain, or other inclement weather has always increased the risk of accidents. Many proposals have been advanced to supplement the situational awareness of the driver/pilot of a boat, automobile, or airplane. For example, it has been proposed to generate a display of nearby terrain from a database having three-dimensional information about the terrain. The derived terrain display may be provided to assist the pilot or driver of the vehicle to maneuver the vehicle during times of low visibility. If used with an aircraft, it is especially advantageous to project the derived terrain display into the pilot's line of sight using a head-up display (HUD) system. When properly aligned with the actual terrain, the derived terrain display enhances the vision of the pilot.
FIG. 1 is a view of a derived or artificial terrain display. It can be seen that the terrain comprises a network of lines 6 that interconnect to form a plurality of elements 8, such as quadrilaterals or triangles, in the form of a grid. In the display shown in FIG. 1, each grid element 8 defines a substantially equal surface area of the terrain. Grid elements appearing larger represent terrain that is relatively close to the viewer, and grid elements appearing smaller represent terrain that is relatively further away from the viewer. As a viewer approaches a portion of the terrain, the grid elements representing that terrain portion increase in size and appear to move toward the viewer.
One challenge of using derived or artificial terrain displays is that distant features appear to be closer than they really are. The driver or pilot cannot easily distinguish between dangerous terrain in close vicinity of the vehicle and less important obstacles in the distance. The problem is made worse when the derived terrain display uses few color shades, as is the case with most known HUD systems. Although the relative size of the grid elements provides some depth cues to the driver or pilot, confusion may still result. Also, if a derived terrain display provides a grid that is not comprised of geometric elements having substantially equal surface areas, the relative sizes of the grid elements do not provide any reliable visual depth cues.
It is therefore an object of the invention to increase the situational awareness of a driver or pilot of a vehicle such as an automobile, boat, or aircraft.
It is yet another object to provide depth cues to a driver or pilot viewing an artificial or derived representation of terrain.
A feature of the invention is an increased attenuation of the derived representation of terrain as the terrain increases in distance from a viewer.
Another feature of the invention is the elimination of displayed terrain that is beyond a predetermined distance from the viewer.
An advantage of the invention is increased awareness of relative distances of terrain in a terrain display derived from stored data.